[R] Subsetting by a logical condition and NA's

[Yuelin Li]

Hi, John,

Often I use y[ which(x == 5) ] to bypass the NAs, and
y[ -which(x == 5) ] includes the mismatches and NAs.  In
all cases I have tested it works on both R and Splus,
which I think is worth the extra which().  Also
I think "x %in% c(5)" or match(x, table=5) in R gives you
what you wanted.

Yuelin.


-----  On Mon, 22 Apr 2002, John Miyamoto wrote:

I have run into a general problem with subsetting of which the following
is a simple example.  Suppose that

x <- c(5, NA, 7, 5, NA, 3)
y <- c(1,  2, 3, 4,  5, 6)

I want to extract the values of y for which x = 5, but y[x==5] yields

> y[x==5]
[1]  1 NA  4 NA

I find that y[!is.na(x) & x==5] yields the desired result:

> y[!is.na(x) & x==5]
[1] 1 4

but I am wondering whether there is a general way to specify a logical
condition such that it yields TRUE when the condition is true and FALSE
when the condition is either false or the input data is NA?  For example,
is there a simpler way to produce the same results as y[!is.na(x) & x==5]?

John

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John Miyamoto, Dept. of Psychology, Box 351525
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